There is a known method for detecting, in an input image, a specified image (for example, an image of a face) that is smaller than the input image, by matching a template image that is a template for detecting the specified image to the input image. In this method, a template image of a predetermined size that is smaller than the square input image is moved gradually from the top left to the bottom right of the input image, and repeatedly matched to the input image. Therefore, an issue arises that a comparatively high-performance processor, a large capacity memory, or the like is necessary when attempting to detect the specified image in a short time period.
As a method for solving the above problem, an area (hereinafter referred to as a “detection target area”) that is only a portion of the input image is set as the area for detecting the specified image, and the template image is only matched to the input image in the detection target area. For example, patent document 1 discloses technology using this method.
FIG. 14 is a functional block diagram of an image processing device pertaining to patent document 1.
This image processing device can be used for detecting a vehicle on an ordinary road, etc. The image processing device includes a cutout unit for generating a low resolution image from an image in the detection target area of a high-resolution image that is output by a high-resolution camera, and a detection unit for detecting the vehicle, etc. with use of the low resolution image.
Also, FIG. 15 shows the detection target area in the image processing device pertaining to patent document 1.
FIG. 15 shows the detection target area in the image (high-resolution image) output by the high resolution camera that is mounted so that two lanes moving vertically in the same direction are pictured. In this image processing device, the detection target area is divided into two equal ranges (hereinafter, these ranges is referred to as “matching target areas”), and each time a high-resolution image is sequentially output by the high-resolution camera, an alternate one of the matching target ranges is selected, and detection of the vehicle, etc. is performed with use of the image (the partial image) in the selected matching target area. Since the vehicle is only detected, etc. in the detection target area, even when the size of the input image (the high-resolution image) is comparatively large, this enables suppressing the throughput amount and causing processing to be performed by a processor, etc. that has comparatively low processing power.
Also, patent document 2 is an example of general technology for detecting the specified image by matching the input image and the template image.
FIG. 16 is a functional block diagram of a face detector pertaining to patent document 2.
The face detector includes a template size and input image scale conversion determination unit. The face detector converts (enlarges or reduces) the input image to generate a plurality of images, each of which has been converted according to a different reduction ratio, and then matches each generated image to the template image. This enables detecting the specified image in the input image, even when the size of the specified image in the input image is different from the size of the specified image in the template image.
Patent document 1: Japanese Patent Application Publication No. 2005-173787
Patent document 2: Japanese Patent Application Publication No. 2004-30629